Seeders of this type have generally used either a knife or a cutting sweep which is carried at each of the seeding elements by the frame so as to cut a furrow in the ground into which the seeds are deposited. The depth of seeding is of fundamental importance to the germination and should therefore be very accurately controlled. The seed must be properly placed a required spacing from the soil surface and also taking into account soil surface moisture characteristics and the sub-surface moisture to obtain the optimum germination.
In many seeders the depth of seeding is controlled by mounting the seeding element in fixed position on the frame and then by controlling the height of the frame relative to the ground as accurately as possible by providing a frame which can flex at different positions so the height of the frame varies to follow as accurately as possible the contours of the ground. However this approach has of course its limitations in that the frame necessarily must have some structural stability which thus limits its ability to totally follow the contours of the ground. Thus some of the seeding elements will at various times provide a depth of seeding which is too deep and other times the depth will be too shallow.
Other commercially available seeding systems are provided in which the seeding elements are individually mounted upon the frame so that they can individually follow the contours of the ground.